The present invention relates to a solid phase catalyst and more particularly to a catalyst for the vapor phase carbonylation of alkyl alcohols, ethers and ester-alcohol mixtures to produce esters and carboxylic acids. More particularly, the present invention relates to a supported catalyst which includes an effective amount of gold along with a halogen promoter. The catalyst is particularly useful in the carbonylation of methanol to produce acetic acid, methyl acetate and mixtures thereof.
Lower carboxylic acids and esters such as acetic acid and methyl acetate have been known as industrial chemicals for many years. Acetic acid is used in the manufacture of a variety of intermediary and end-products. For example, an important derivative is vinyl acetate, which can be used as monomer or co-monomer for a variety of polymers. Acetic acid itself is used as a solvent in the production of terephthalic acid, which is widely used in the container industry, and particularly in the formation of PET beverage containers.
There has been considerable research activity in the use of metal catalysts for the carbonylation of lower alkyl alcohols, such as methanol, and ethers to their corresponding carboxylic acids and esters, as illustrated in equations 1-3 below:
ROH+COxe2x86x92RCOOHxe2x80x83xe2x80x83(1)
2ROH+COxe2x86x92RCOOR+waterxe2x80x83xe2x80x83(2)
ROR+COxe2x86x92RCOORxe2x80x83xe2x80x83(3)
Carbonylation of methanol is a well-known reaction and is typically carried out in the liquid phase with a catalyst. A thorough review of these commercial processes and other approaches to accomplishing the formation of acetyl from a single carbon source is described by Howard et al. in Catalysis Today, 18 (1993) 325-354.
Generally, the liquid phase carbonylation reaction for the preparation of acetic acid using methanol is performed using homogeneous catalyst systems comprising a Group VIII metal and iodine or an iodine-containing compound such as hydrogen iodide and/or methyl iodide. Rhodium is the most common Group VIII metal catalyst and methyl iodide is the most common promoter. These reactions are conducted in the presence of water to prevent precipitation of the catalyst. However, solid heterogeneous carbonylation catalysts offer the potential advantages of easier product separation, lower cost materials of construction, facile recycle, and even higher rates. The use of solid carbonylation catalyst in a vapor phase carbonylation reaction is especially beneficial due to the fact that operating in the vapor phase eliminates catalyst dissolution, i.e., metal leaching from the catalyst support, which occurs in the known heterogeneous processes operating in the presence of liquid compounds.
Rhodium was the first heterogeneous catalyst used in vapor phase carbonylation. Schultz, in U.S. Pat. No. 3,689,533, discloses using a supported rhodium heterogeneous catalyst for the carbonylation of alcohols to form carboxylic acids in a vapor phase reaction. Schultz further discloses the presence of a halide promoter. Schultz in U.S. Pat. No. 3,717,670 goes further to describe a similar supported rhodium catalyst in combination with promoters selected from Groups IB, IIIB, IVB, VB, VIB, VIII, lanthanide and actinide elements of the Periodic Table. Schultz teaches that these elements are useful to promote the rhodium activity, but do not themselves provide carbonylation catalysis. Uhm, in U.S. Pat. No. 5,488,143, describes the use of the alkali metals Li, Na, K, Rb, and Cs, the alkaline earth metals Be, Mg, Ca, Sr, and Ba, or the transition metals Co, Ru, Pd, Pt, Os, Ir, Ni, Mn, Re, Cr, Mo, W, V, Nb, Ta, Ti, Zr, and Hr as promoters for supported rhodium for the halide-promoted, vapor phase methanol carbonylation reaction. Further, Pimblett, in U.S. Pat. No. 5,258,549, teaches that the combination of rhodium and nickel on a carbon support is more active than either metal by itself.
Iridium is also an active catalyst for methanol carbonylation reactions but normally provides reaction rates lower than those offered by rhodium catalysts when used under otherwise similar conditions. In addition to the use of iridium as a homogeneous alcohol carbonylation catalyst, Paulik et al., in U.S. Pat. No. 3,772,380, describe the use of iridium on an inert support as a catalyst in the vapor phase, halogen-promoted, heterogeneous alcohol carbonylation process.
Evans et al., in U.S Pat. No. 5,185,462, describe heterogeneous catalysts for halide-promoted vapor phase methanol carbonylation based on noble metals attached to nitrogen or phosphorus ligands attached to an oxide support.
Nickel on activated carbon has been studied as a heterogeneous catalyst for the halide-promoted vapor phase carbonylation of methanol, and increased rates are observed when hydrogen is added to the feed mixture. Relevant references to the nickel-on-carbon catalyst systems are provided by Fujimoto et al. in Chemistry Letters (1987) 895-898 and in Journal of Catalysis, 133 (1992) 370-382 and in the references contained therein. Liu et al., in Ind. Eng. Chem. Res., 33 (1994) 488-492, report that tin enhances the activity of the nickel-on-carbon catalyst. Mueller et al., in U.S. Pat. No. 4,918,218, disclose the addition of palladium and optionally copper to supported nickel catalysts for the halide-promoted carbonylation of methanol. In general, the rates of reaction provided by nickel-based catalysts are lower than those provided by the analogous rhodium-based catalysts when operated under similar conditions.
Other single-metals supported on carbon have been reported by Fujimoto et al. in Catalysis Letters, 2 (1989) 145-148 to have limited activity in the halide-promoted vapor phase carbonylation of methanol. The most active of these metals is Sn. Following Sn in order of decreasing activity are Pb, Mn, Mo, Cu, Cd, Cr, Re, V, Se, W, Ge and Ga. None of these other single metal catalysts is nearly as active as those based on Rh, Ir, or Ni.
U.S. Pat. No. 5,218, 140, to Wegman, describes a vapor phase process for converting alcohols and ethers to carboxylic acids and esters by the carbonylation of alcohols and ethers with carbon monoxide in the presence of a metal ion exchanged heteropoly acid supported on an inert support. The catalyst used in the reaction includes a polyoxometallate anion in which the metal is at least one of a Group V(a) and VI(a) is complexed with at least one Group VIII cation such as Fe, Ru, Os, Co, Rh, Ir, Ni, Pd or Pt as catalysts for the halide-free carbonylation of alcohols and other compounds in the vapor phase. The process does not utilize a halide cocatalyst.
Various solid support materials have been reported as useful in halide-promoted heterogeneous vapor phase carbonylation systems. European Patent Applications EP 0 120 631 A1 and EP 0 461 802 A2 describe the use of special carbons as supports for carbonylation catalysts having a single transition metal component chosen from Co, Ru, Fe, Ni, Rh, Pd, Os, Ir, Pt, and Group VIII metals. The literature contains several reports of the use of rhodium-containing zeolites as vapor phase alcohol carbonylation catalysts at one bar pressure in the presence of halide promoters. The lead references on this type of catalyst are presented by Maneck et al. in Catalysis Today, 3 (1988), 421-429. Gelin et al., in Pure and Appl. Chem., Vol 60, No. 8, (1988) 1315-1320, provide examples of the use of rhodium or iridium contained in zeolite as catalysts for the vapor phase carbonylation of methanol in the presence of halide promoter. Krzywicki et al., in Journal of Molecular Catalysis, 6 (1979) 431-440, describe the use of silica, alumina, silica-alumina and titanium dioxide as supports for rhodium in the halide-promoted vapor phase carbonylation of methanol. Luft et al., in U.S. Pat. No. 4,776,987 and in related disclosures, describe the use of chelating ligands chemically attached to various supports as a means to attach Group VIII metals to a heterogeneous catalyst for the halide-promoted vapor phase carbonylation of ethers or esters to carboxylic anhydrides Drago et al., in U.S. Pat. No. 4,417,077, describe the use of anion exchange resins bonded to anionic forms of a single transition metal as catalysts for a number of carbonylation reactions including the halide-promoted carbonylation of methanol.
A number of solid materials have been reported to catalyze the carbonylation of methanol without the addition of the halide promoter. Gates et al., in Journal of Molecular Catalysis, 3 (1977/78) 1-9, describe a catalyst containing rhodium attached to polymer bound polychlorinated thiophenol for the liquid phase carbonylation of methanol.
Smith et al., in European Patent Application EP 0 596 632 A1, describe the use of mordenite zeolite containing Cu, Ni, Ir, Rh, or Co as catalysts for the halide-free carbonylation of alcohols. Feitler, in U.S. Pat. No. 4,612,387, describes the use of certain zeolites containing no transition metals as catalysts for the halide-free carbonylation of alcohols and other compounds in the vapor phase.
Certain disadvantages present in the prior art include instability of the carbonylation catalysts, lack of product selectivity and difficult product separation. Therefore, there is a need for an alternative catalyst which can be used in a vapor phase carbonylation process for the production of carboxylic acids and their esters and in which the catalyst is maintained in the solid phase.
Briefly, the present invention relates to a solid supported catalyst for producing esters and carboxylic acids in a vapor phase carbonylation process and a process for making the catalyst composition. Suitable reactants for contacting the solid catalyst include lower alkyl alcohols, ethers and ester-alcohol mixtures. The catalyst includes a catalytically effective amount of gold. The gold is associated with a solid support material which, desirably, is inert to the carbonylation reaction. The catalyst further includes a halogen promoter.
It is an object of the invention to provide a carbonylation catalyst composition having gold associated with a solid support material.
It is another object of the invention to provide a solid phase catalyst composition for vapor phase carbonylation of methanol to form acetic acid or methyl acetate.
Another object of the invention is to provide a more selective and reactive carbonylation catalyst composition for the production of carboxylic acids.
Yet another object of the invention is to provide a catalyst composition which results in higher yields of acetic acid with minimum formation of ethers, aldehydes, and other undesirable by-products.
These and other objects and advantages of the invention will become apparent to those skilled in the art from the accompanying detailed description.